1. Technical Field
The present invention relates generally to synthetic chemistry. More particularly, the present invention relates to poly(thioesters), monomeric diesters and their derivatives. Further, the field of this invention is polysulfur-containing polymeric ester compositions and their polymers.
2. Background of the Invention
Despite the mature nature of the field of polymers, there remain many opportunities to create polymers having novel properties and applications. Polymers may be divided into addition polymers and condensation polymers. Among the condensation polymers are polyesters, polyethers, polyurethanes, polyamines, and polyanhydrides. These polymers find wide application in areas of molded products, lubricants, sealants, coatings, paints, films, fibers, elastomers and other formulations. Their properties vary widely depending upon the functional groups employed, both as to nature and diversity, the backbone units, the functionalities in the backbone, the molecular weight and homogeneity of molecular weight range of the polymeric molecules, and the like. Because of the great diversity of properties of the polymers, there can be numerous customized applications for the polymers, where the properties of the polymers are customized to a particular need.
Polymers containing polythioalkyl groups have not found extensive employment in the polymeric field, with the exception of the Thiokol® polymers that currently are not widely used due to environmental concerns. Yet, the presence of sulfur in the polymers can have desirable properties. Some polymeric products containing polysulfide linkages have been reported for a variety of purposes, such as polymers having disulfide and ether groups, disulfide and carbamate groups, and disulfide and acetal groups in the polymer backbone. There have been reports of other polymeric compositions, where the disulfide is in a side chain of the polymer, as in addition polymers of acrylics. While specific compounds having sulfides having greater than one sulfur are disclosed in the literature, for the most part they are not exemplified in the experimental work. Specifically, there have been no reports of polymers employing a monomeric unit of a polysulfide functionality in the backbone and formed from a combination of a polysulfide-containing diol and a dibasic acid.
Relevant Literature
Ethers of di(hydroxyethyl)sulfide and -disulfide are reported in U.S. Pat. No. 2,582,605. Polymers of alkyldisulfides terminating in hydroxyl groups and further reacted with polyurethanes are reported in U.S. Pat. No. 3,386,963. Polymers of polymerized thiodiglycol reacted to provide terminal halide groups which are then further reacted with sodium polysulfide to form a latex dispersion are reported in U.S. Pat. No. 4,124,645. Polymers of polymerized sulfide and polysufide glycols terminated with mercaptans are reported in U.S. Pat. No. 4,764,299. U.S. Pat. No. 6,383,324 reports the polymerization of a “randomly copolymeric polyacetal of a dithiodialkylene glycol” with polyisocyanates. Sulfur substituted acrylic polymers are reported in U.S. Pat. Nos. 4,131,716 and 6,114,485.
Hydroxyl groups that are in the β-position relative to a sulfur atom in an aliphatic chain have unusually high reactivity, and their properties are significantly different from other hydroxyl groups. For example, unlike compounds with hydroxyl groups in other positions, compounds with hydroxyl groups in the β-position relative to a sulfur atom in an aliphatic chain readily undergo self-polycondensation as well as co-condensation with other glycols in the presence of other acids and/or at elevated temperatures, resulting in the formation of poly(thioethers) (F. Richter, et. al., U.S. Pat. No. 2,582,605).
Di(hydroxyethyl)disulfide, as well as other di(hydroxyethyl)polysulfides are typical compounds with hydroxyl groups in the β-position relative to a sulfur atom. They are known in the art to be precursors for various poly(thioethers), which have been used in lubricants (U.S. Pat. No. 2,582,605), in polyurethanes (U.S. Pat. No. 3,386,963), in mercaptan-terminated oligomers (U.S. Pat. No. 4,124,645), in transmission fluids (U.S. Pat. No. 4,764,299), and in acetal-functional compounds used in window insulation (U.S. Pat. No. 6,383,324).
The prior art describes several attempts to convert di(hydroxyethyl)polysulfides into various compounds that contain ester functionality adjacent to the —(CH2)n—S— segment. For example, U.S. Pat. No. 6,114,485 discloses compounds that include an —O—C(O)—(CH2)2—S— segment in monomeric products, but the chemical structure of these compounds is achieved through a chain of several complex chemical reactions that take multiple steps and over 20 hours of combined reaction time. In addition, the technology described in this patent cannot be used to produce polymeric products with multiple poly(thioester) segments.
U.S. Pat. Nos. 2,221,418 by Weihe et al. (referred to hereafter as Weihe) and 5,407,972 by Smith et al. (referred to hereafter as Smith) describe products that are produced after (polythio)glycols are mixed with dicarbonic acids and/or their anhydrides. However, these patents do not describe the formation of poly(thioesters) from these products. For example, Weihe describes the formation of an “insoluble balsam”, and Smith describes “polysulfide polymers” produced as the result of the interaction between di(hydroxyethyl)polysulfides and dibasic carbonic acids or their anhydrides.
Nowhere in Weihe or Smith is described the chemical structure of the resulting products. However, based on the above-described unusual reactivity of hydroxyl groups in the β-position relative to a sulfur atom, and the strong tendency of such hydroxyl groups to homo-condense according to reaction (1), it is highly likely that the products formed by Weihe and Smith under the conditions described in these patents are poly(thioethers), rather than poly(thioesters).mHO—(CH2)2—Sx—(CH2)2—OH→H(—O—(CH2)2—Sx—(CH2)2)m—OH+(m−1)H2O  (1)
In the case where the products were formed with the participation of dibasic carbonic acids, they would likely form a solution of dibasic carbonic acids in solid or semi-solid poly(thioether) resins. In the case where the products were formed with the participation of anhydrides of dibasic carbonic acids, the solid or semi-solid poly(thioether) resins would have a chance to react with anhydrides. This would allow the formation of a randomly-formed compound with no more than two radicals per molecule and a single ester structure for each radical. A regular poly(thioester) polymer would not be formed.
The absence in the prior art of the description of regular poly(thioesters) produced from compounds with hydroxyl groups in the β-position relative to a sulfur atom is further illustrated by Wilson in U.S. Pat. No. 5,342,724 (referred to hereafter as Wilson). Wilson describes the formation of multiple poly(thioesters) from sulfur-containing diols and dibasic carbonic acids. However, all sulfur-containing diols with hydroxyl groups in the β-position relative to the sulfur atoms were left out from the list of diols mentioned by Wilson, as the state-of the art technology available at the time did not allow production of poly(thioesters) from such compounds.
Accordingly, there is a need in the art to develop methods of forming poly(thioesters) from sulfur-containing diols with hydroxyl groups in the β-position relative to the sulfur atoms.